This invention relates to the field of robotic systems and to the use of such systems in military environments including uses having load variation.
Although robotic systems have achieved a significant degree of acceptance in certain well-controlled environments such as in repetitive manufacturing materials handling and the remote handling of dangerous materials, it is generally accepted in the robotic systems art that such systems perform best when exposed to predictable load demands and linear torque requirements, that is, torque requirements which are not varied according to such real-life effects as Coulomb friction, starting friction, gravity variations, and changes in the mass of the workpiece being transported by the robotic system.
In the military environment where a robotic system would be of major assistance in the loading of ordnance on a military aircraft or in the replacement of aircraft components on a flight line, such repetitive loading and controlled environment conditions are the exception rather than the rule of use. Such military robotic systems are contemplated to especially be susceptible to load variations and to torque linearity difficulties and other mismodeled effects or nonlinearities entering into their equations of motion. In such systems, additional losses due to nonlinear friction, gravity and other effects are found to provide an error between the actual output trajectory of the system, .alpha.(t), and the desired output trajectory of the system, .alpha..sub.d (t).
A previous effort to solve problems of this type has resulted in the computed torque method of reducing error in a robotic system. The computed torque method is described in the robotic literature, including the description presented in chapter 8 of the text "Introduction to Robotics, Mechanics and Control", by John J. Craig, Addison Wesley Publishing Co., 1986, the contents of which are hereby incorporated by reference herein. Generally, the computed torque method of error reduction and in a robotic system is found to require exact knowledge of the nonlinearity condition affecting the robot performance and a measurement of the robotic system output, .alpha.(t), together with all of its time derivatives. Requirements of this refinement are somewhat difficult to achieve in a practical robotic system, especially the measurement of second derivatives of the system output position, that is, the acceleration of the system output member at any point along its path of travel.
The prior patent art also includes several examples of robotic systems that are concerned with the reduction of output error. Included in these patents is U.S. Pat. No. 4,362,972 of R. C. Evans et al., a system in which the robot's output performance is compared with an independent system of measurement and differences between this independent measurement system and the robot performance are used to improve the robot's performance. These patents also include U.S. Pat. No. 4,437,045 issued to P. Mitsuoka and concerned with the use of a model reference adaptive system in controlling a servomechanism. Also included is the patent of T. Maruo et al., U.S. Pat. No. 4,737,697, which is concerned with the manual teaching of a robotic system during a learning or teaching mode of operation and the imposition of deliberate differences between the learning and playback mode operations of the system.
Also included in these prior patents is the patent of M. Yoshida et al., U.S. Pat. No. 4,737,905, which is concerned with the movement of a driven member such as a machine stage in response to commands received at a joystick controller and including the use of nonlinear transforming circuitry. Additionally included is U.S. Pat. No. 4,763,276 of N. D. Derreirra et al., which is concerned with the refinement of an original command signal in order to improve the robot's output performance. Also included is U.S. Pat. No. 4,791,588 issued to N. Onda et al., which is concerned with the combining of an environmental information input signal with a command signal in order to achieve a high precision position control.
Although these prior art references indicate a considerable degree of attention to the improvement of robotic system performance and reduction of system errors, none is suggestive of the simplified and productive majorizing function addition of a supplemental torque to the normal output of a robotic system as taught in the present invention.